Plastic dust tube for shock absorber

ABSTRACT

Telescopic shock absorber having a cup-like metallic cover plate with a cylindrical rim having a series of arcuately spaced and inwardly projecting dust tube retainer tangs. The dust tube is formed from a generally rectilinear blank of flexible plastic material having a series of holes punched along the upper edge thereof spaced to match the retainer tangs. The blank is curled into cylindrical tube that is subsequently inserted into the cover plate and turned until the retainer tangs enter corresponding holes in the upper end of the tube so that the tube is fixed to the cover plate.

This invention relates to shock absorbers and more particularly to a newand improved plastic dust tube and metallic cover plate assembly for ashock absorber for vehicles and to a new and improved method of curlingand attaching a plastic dust tube to the shock absorber cover plate.

In the preferred embodiment of this invention, the dust tube is formedfrom a sturdy and flexible thermo-plastic material such as polypropylenestock in individual sheet form. Such stock can be produced economicallyby well known extrusion or rolling methods and stamped into generallyrectilinear blanks. In this invention, the dust tube blank preferablyhas a plurality of equally spaced openings along one edge thereof sothat they will receive retainer tangs struck radially inwardly from anouter rim of a metallic cover plate. If desired, the opposite side edgesof the blank could be formed with spaced tabs which interlace orinterlock with one another when the blank is curled into a tube. A pairof special dies can be employed to curl the blank around the outerperiphery of a shock absorber so that the tabs interlace with oneanother. Using the shock absorber as a backing, the mating andoverlapping parts of the curled blank can be seam welded ultrasonicallyor by other suitable means to complete the dust tube. After beingwelded, the shock and dust tube are removed from the dies and the dusttube is forced axially into the cover plate and turned until theretainer tangs enter the openings at the upper edge thereof.

With this invention, a new and improved wrapped and seamed plastic dusttube is provided for a hydraulic shock absorber for vehicles to reduceweight and costs. This plastic dust tube allows the shock absorbercomponents to be fully assembled prior to dust tube assembly. With theplastic dust tube fitting into the end cap, external fasteners andprojections are eliminated. Furthermore, the shock absorber may becompleted and treated with rust preventitives prior to insertion of thedust tube into the cap. The dust tube of this invention can be used withvarious types and sizes of shock absorbing mountings and prevents metalto metal contact between the shock absorber reservoir tube andsurrounding suspension springs.

These and other features, objects and advantages of this invention willbe more apparent from the following detailed description and drawings inwhich:

FIG. 1 is a vertical side view partly in cross section of a telescopicshock absorber for a vehicle having a metallic cover plate and plasticdust tube;

FIG. 2 is a side elevational view of the shock absorber of FIG. 1;

FIG. 3 is a top plan view of a first embodiment of a dust tube blank;

FIGS. 4, 5, 6 and 7 are diagrammatic end views illustrating the methodin which the dust tube is installed around the exterior of a cylindricalshock absorber; and

FIG. 8 is a top plan view of a second embodiment of the dust tube blank.

As shown in FIG. 1, there is a shock absorber 10 having an interiorpressure cylinder 12 closed at its upper end by a rod guide 14. Thepressure cylinder receives a reciprocally movable piston 15 which iscarried on the end of the piston rod 16 that extends upwardly throughthe rod guide 14 and outwardly from the upper end of the shock absorber10. The upper end of the piston rod carries a conventional mounting, notshown, for attachment with a spring portion of a vehicle.

A reservoir tube 18 surrounds and is radially spaced from the pressurecylinder 12 to form a reservoir 20 for hydraulic fluid employed as thedamping medium of the shock absorber. The upper end of the reservoirtube 18 has a cup-like end cap 24 secured thereto which seats againstthe upper cylindrical end 26 of the rod guide 14. The opposite end ofthe reservoir tube 18 is closed by a cap 28 having a mounting ring 30fastened thereto for vehicular attachment to an unsprung portion of avehicle.

The upper end of rod guide 14 has a chamber 32 receiving a resilientelastomer rod seal 34 held under compression by helical spring 36disposed between the rod guide and the lower end of the rod seal. Theseal chamber 32 is hydraulically connected to the reservoir 20 throughan opening 38 formed in the rod guide and one or more passages 40 formedbetween the end cap 24 and the outer periphery of the rod guide 14. Thepiston rod 16 extends through the rod seal 34 and end cap 24 and carriesa cup-like metallic cover plate 44 secured thereto by welded collar 46.The cover plate has an annular downwardly-extending rim 48 forming areceptacle for the upper end of a cylindrical flexible dust tube 50 ofpolypropylene or other suitable plastic which extends downwardly andaround the reservoir tube as shown in FIGS. 1 and 2. The cover plate anddust tube assembly shields and protects the components interior thereoffrom dust, dirt, stones or other road hazards. The cover plate has aplurality of arcuately spaced tangs 52 lanced inwardly from the annularrim 48 for attachment of the dust tube.

FIG. 3 illustrates the flexible plastic sheet stock or blank B used toform the dust tube. The blank has a series of laterally spaced circularopenings 54 punched or otherwise formed adjacent to the upper edgethereof. These openings are sized and spaced to receive the retainertangs 52 once the stock or blank B is curled into its tubular formationand inserted endwise into the cover plate. To facilitate joining theside edges of the blank B, each of the side edges are preferably formedwith a series of spaced tabs 56 and 58 respectively. In addition tobeing spaced, the side edge tabs 56 and 58 are offset with respect toone another so that they will interlace with each other as shown in FIG.2 when the blank is curled into its tubular form. After being curled,the tabs 56 and 58 are welded ultrasonically as indicated by weldments Wto the underlying portion of the tube. Once the tube 50 is curled andwelded, it can be inserted axially into the cap 44 and turned until theretainer tabs 50 enter the circular openings 54 formed in the upper edgeof the blank. With the tabs 50 extending through the circular opening asshown in FIG. 1, the plastic dust tube will be retained in position.

Instead of being formed from the blank B of FIG. 3, the dust tube couldbe readily formed by blank B' of FIG. 8. This blank is similar to blankB in that it has circular openings 64 adjacent to the upper edge thereofand has a series of spaced side tabs 66 and 68 extending from oppositeside edges thereof. Tabs 66 and 68, undercut at 69 and 71, are offsetfrom one another. With this construction, the tabs 66 and 68 can fitinto their respective undercuts so that the blank can be locked in itstubular formation after it has been curled. While not required, thecurled blank B could be ultrasonically welded as described above ortaped or otherwise secured so that the side edges are more positivelyfastened to one another. After being fastened in a suitable manner suchas described above, the dust tube is axially inserted into the end capand rotated. The upper end of the dust tube is deflected by the retainertangs of the cover plate until they find the retainer holes 64 andsecure the dust tube in position.

FIGS. 4-7 diagrammatically illustrate a preferred method for curling thedust tube around the cylindrical reservoir tube of the shock absorberand for fastening the ends of the dust tube together at the matingedges. As shown in FIG. 4, the flat blank B or B' is fed onto a lowerdie D which is spaced vertically from an upper die D'. The lower die Dis formed with a semi-cylindrical recess 70 which underlies the blankfor accommodating the shock absorber which at this time is completelyassembled with the exception of the dust tube. The shock absorber is feddownwardly from its intermediate position between dies D and D' bysuitable feeder mechanisms, not shown, to the FIG. 5 position. As theshock absorber enters the recess 70, the blank B is forced into therecess 70 and the side edges of the blank will extend upwardly so thatthe blank generally has a U-shaped conformation in cross section. Theupper die D' is subsequently moved downwardly toward die D. As thismovement progresses, the side edges of the dust tube are forced towardone another. The upper die is formed with ramps R which correspond tothe tabs 56, 58 or 66, 68 which turn the tabs inwardly as best shown inFIG. 6 so that they interlace with one another. After the tabs areinterlaced with one another, suitable welding units U are introducedthrough openings in the upper die D and the overlapped portions of theblank are welded together. It will be seen that the reservoir tube isused as a backing for this procedure. After being welded, the weldingunits are removed and the dies opened so that the part with the dusttube surrounding the reservoir can be removed from the dies. Afterremoval, the dust tube is inserted axially into the end cap and fastenedthereto as previously stated.

It will be appreciated while this invention has been described with tabson the side edges of the blanks for interlacing, the device could bemade by curling so that straight edges thereof overlap for connection bysuitable seam welding.

This invention is not limited to the particular details of constructionand the method shown and described for purposes of illustrating theinvention for other modifications and method falling within the scope ofthe appended claims will occur to those skilled in the art.

I claim:
 1. A shock absorber comprising an elongated pressure cylinderhaving a hydraulic fluid therein, a piston mounted for reciprocatingmovement in said cylinder, a piston rod operatively connected to saidpiston and extending from one end of said cylinder, a cover plate, meanssecuring said cover plate to said rod external of said cylinder, anannular skirt extending angularly from the outer radial limit of saidcover plate, arcuately spaced fastener means secured to said annularskirt and extending radially inwardly therefrom, a flexible plastic dusttube adapted to extend downward from said cover plate to surround aportion of said piston rod and said cylinder, said dust tube beingformed from a sheet of plastic stock material, said sheet having firstand second side edges each with a series of spaced finger-like tabsextending outwardly therefrom, said tabs of said first series beingoffset with respect to said tabs of said second series, said dust tubebeing curled into a cylinder with the tabs of said first series beinginterlaced with the tabs of said second series to thereby interconnectsaid first and second edges to one another, said sheet having an upperedge and having a plurality of openings formed therein adjacent saidupper edge providing receptacle means, said receptacle means receivingsaid fastener means so that one end of said plastic dust tube is securedwithin said cover plate and said dust tube is held in fixed positionradially outwardly of said pressure cylinder.
 2. A shock absorbercomprising an elongated pressure cylinder having a hydraulic fluidtherein, a piston mounted for reciprocating movement in said cylinder, apiston rod operatively connected to said piston and extending from oneend of said cylinder, a metallic cover plate operatively secured to saidpiston rod external of said cylinder, said cover plate having an annularskirt extending downwardly from the outer radial limits thereof, aplurality of arcuately spaced tangs integral with and extending radiallyinwardly from said annular skirt, a flexible plastic dust tube securedto said skirt and extending downwardly from said cover plate to surrounda portion of said piston rod and said cylinder, said dust tube beingformed from a generally rectilinear sheet of plastic stock material,said sheet having first and second side edges each with a series ofspaced finger-like tabs extending laterally therefrom, said tabs of saidfirst series being horizontally offset with respect to the tabs of saidsecond series, said sheet being curled into a cylinder to form said dusttube, said tabs of said first series being interlaced with the tabs ofsaid second series to thereby interconnect said first and second sideedges to one another, said dust tube having an upper edge, a pluralityof openings formed in said dust tube adjacent said upper edgecorresponding to and receiving the tangs extending from said cover plateto thereby connect said dust tube to said cover plate.